I have a cell with the following contents:
=CONCATENATE("Last updated ",TEXT(LastSaved(), "mmmm dd, yyyy"))

LastSaved is a UDF with the following definition:

Public Function LastSaved()
LastSaved = ActiveWorkbook.BuiltinDocumentProperties("Last Save Time")
End Function

I have automatic recalc turned on. If I save the workbook, exit and bring
it up again, the cell value still shows the previous last saved date. If I
F2 on the cell and press Enter, the date is refreshed with the current date.
What's going on?